Shell script - LFTP

I using crontab that run script on each morning to collect lots of text file from a server and send them to FTP server as one tar file(about 600MB).
I would like to copy this one tar file from the FTP server to a local machine, but first I need to check each hour that the tar file is found on the FTP server.
Meaning is that I need to connect to the FTP server hourly and check if the tar file exist.
I'm using lftp and using the command lftp -f FileNameWhichContainTheBelow